To enhance steering stability performance, conventionally, the land portion width of a tread portion is made large so as to ensure tread rigidity. However, an excessively large land portion width results in reduced ground contact pressure at the center position in the tire width direction of the land portion. Accordingly, both end portions in the tire circumferential direction at substantially the center position deform inward toward the land portion. As a result, the footprint length is shortened causing contact with the ground and steering stability performance to be degraded.
Technology relating to enhancement of steering stability performance accompanying enhanced contact with the ground is known (see Japanese Unexamined Patent Application Publication No. 2002-029216A). In such technology, straight-line stability performance, a kind of steering stability performance, is enhanced by forming a land portion in a curved shape protruding outward in the tire radial direction.
As described in Japanese Unexamined Patent Application Publication No. 2002-029216A, by forming a land portion in a curved shape protruding outward in the tire radial direction, contact with the ground is enhanced. Note that the method of determining the curved shape described in Japanese Unexamined Patent Application Publication No. 2002-029216A employs one type of road contact surface profile line extending over the whole of the tread surface in the tire width direction.
In recent years, development of a pneumatic tire having superior steering stability performance as well as superior hydroplaning resistance performance and uneven wear resistance performance has been in demand.